Technical Field
The present disclosure relates to a driving method for an image pickup device and a driving method for an imaging system.
Description of the Related Art
An image pickup device has been known which includes a plurality of pixels and a vertical signal line which receives signals from a plurality of pixels.
In an image pickup device according to Japanese Patent Laid-Open No. 2010-259027, each of a plurality of pixels has a photoelectric conversion unit, a floating diffusion (hereinafter, called an FD unit) which accumulates electric carriers generated by the photoelectric conversion unit, and an amplifying transistor which outputs a signal according to voltage in the FD unit. Each of the plurality of pixels further has a selection transistor which switches between a conductive state and a non-conductive state between the amplifying transistor and the vertical signal line.
In the image pickup device according to Japanese Patent Laid-Open No. 2010-259027, a current source is connected to the vertical signal line, and electric current is supplied to an amplifying transistor in pixels in conduction brought by a selection transistor. An amplifying transistor has a main node which is different from a main node connected to the selection transistor and receives supply of voltage from a voltage source. When the selection transistor is brought into conduction, a current source, an amplifying transistor and a voltage source configure a source follower circuit.
A plurality of pixels are arranged across a plurality of rows and a plurality of columns. The image pickup device disclosed in Japanese Patent Laid-Open No. 2010-259027 performs a first operation which brings selection transistors in pixels of a plurality of rows into conduction in parallel and mixes signals output by amplifying transistors in the plurality of pixels in a vertical signal line. The image pickup device disclosed in Japanese Patent Laid-Open No. 2010-259027 further operates a second operation which sequentially brings selection transistors in the pixels of each of the rows. Thus, the amplifying transistors of the pixels output.
Japanese Patent Laid-Open No. 2013-211832 discloses a configuration having a column signal processing circuits provided for each of a plurality of columns of pixels. The column signal processing circuit outputs a signal acquired by amplifying in accordance with an amplification factor a signal output from the corresponding pixel to the vertical signal line.
As a difference between signals output by a plurality of amplifying transistors increases, the accuracy of signal acquired as a result of the first operation decreases. Under some imaging condition, a difference between signals to be mixed may easily increase. Both of Japanese Patent Laid-Open No. 2010-259027 and Japanese Patent Laid-Open No. 2013-211832 do not consider an operation in a case where a difference between signals to be mixed is large.